The present invention relates to a method and apparatus for use in connecting a multi-line fluid conduit carried by a remotely operated vehicle (ROV) or directly connected to a surface vessel to a subsea equipment assembly such as an hydraulically actuated device.
U.S. Pat. No. 4,682,931 describes a system for effecting a fluid connection between a subsea wellhead assembly and the surface so that hydraulic pressure may be supplied to the well head assembly to actuate various devices. As described in the patent, the system comprises a receptacle which is mounted on the subsea wellhead and provided with suitable hydraulic ports to which fluid may be supplied to effect the desired operations. A probe or stab sub is inserted into the receptacle and is provided with hydraulic ports that align with the ports in the receptacle when the stab sub is properly positioned. The stab sub is held in place by a vacuum means while an effective seal is provided between the stab sub and the receptacle by "O" rings or similar sealing devices.
In U.S. Pat. No. 4,863,314 there is described a hydraulic connection similar to that described in the above patent but with provisions for making a frictionless connection. As explained in this patent, the force that can be exerted by an ROV is very limited since it has nothing to react against to exert force. Thus, the use of "O" rings for effecting a seal between the stab sub and the receptacle is limited to those cases where the force required to insert the stab sub is in the range of 30 pounds. This effectively eliminates the use of conventional "O" rings in a subsea environment if the stab sub has a diameter greater than approximately one inch. For example, as the stab sub approaches 4 inches in diameter, the force required to insert it using conventional "O" ring construction in the receptacle would exceed 100 pounds.
The '314 patent solves the problem by providing a frictionless connection which is easily inserted into the receptacle and then utilizes mechanical means for forcing a seal means into contact with the receptacle. More particularly, the patent discloses the use of "O" rings which are retracted to a first position in which their outer diameter is equal to or less than the diameter of the stab sub and are then expanded outwardly to effect a seal. The "O" rings are expanded by means of a sleeve which is moved axially with respect to the stab sub to force the "O" rings into a sealing engagement with the wall of the receptacle. While the invention of the '314 patent solves the problem of providing an hydraulic stab sub which may be inserted into a receptacle mounted on a subsea wellhead, it does have several problems. For example, the invention utilizes an axial sleeve which must be reciprocated within the stab sub to move the "O" rings into a sealing position. The use of the reciprocating sleeve is undesirable in subsea equipment since it can be rendered inoperative by debris which may enter into the stab sub. Further, the axial sleeve requires considerable force to move in order to move the "O" rings into sealing engagement. Also, there is reliance upon the elasticity of the "O" rings to effectively retract them after the sleeve has been moved to a position in which the "O" rings can retract into their original shape. In cases where the stab sub has been in position for an extended period of time, the possibility exists that the axial sleeve will not retract to allow the "O" rings to retract to their original position. Thus, the stab sub will be effectively stuck in the receptacle.